1. Field of the Invention
The present invention relates generally to cushioning mechanisms suitable for use with chairs such as office chairs and, more particularly, to cushioning mechanisms for their seat portions as well as interlocking cushioning mechanisms for supporting the seat portions to allow integral movement with their backrests.
2. Description of the Related Art
It is known that such a cushioning mechanism for a seat portion used, e.g., for an office chair typically incorporates a cushioning member such as a gas spring, a coil spring or a torsion bar.
Various types of interlocking cushioning mechanisms for supporting seat portions and backrests of chairs such as office chairs in an integral movable fashion have also heretofore been proposed. In such a conventional type of interlocking cushioning mechanism, the cushioning member for the seat portion is constituted by a gas spring, a coil spring or a torsion bar, and the cushioning member is linked with the backrest by a suitable link mechanism in an interlocking manner such as to mitigate the shock of the swinging motion of the backrest. Such an interlocking cushioning mechanism is disclosed, for example, in U.S. Pat. No. 4,533,177, Japanese Patent Laid-open No. 29304/1986, and Japanese Utility Model Laid-open No. 184451/1986.
It is also known that such a seat-portion cushioning mechanism employing a spring-type cushioning member has a mechanism that is arranged to allow users to alter the degree of hardness and the magnitude of resilient force of the cushioning member. However, this mechanism has a complicated structure and a large size and thus requires a large number of parts. As a result, the spring-tupe cushioning member involves various failure factors and its motion is likely to lack smoothness.
In particular, cushioning mechanisms of the type employing a spring incorporated in the frame of a support portion or a seat portion of a chair require complicated structures.
In addition, conventional types of interlocking cushioning mechanisms for supporting seat portions for integral movement with backrests in an interlocking manner involve the problem that their interlocking mechanisms are complicated. Interlocking cushioning mechanisms of another type which allows users to alter the degree of cushioning effect, such as the hardness or resilient force of a spring incorporated therein, require a complicated structure and a large size as well as a large number of parts. As a result, this type of mechanism involves various failure factors and its motion is likely to lack smoothness.